High vacuum



May 30, 1961 A. A. LAN DFORS HIGH VACUUM Filed March 4, 1959 I I I I I II I x I %w& ll \v\ t I I I I I S r I I II I I vw mm mw an vn NN\\ q 155% N wt Q Q? Uni ed Stat Pat n Q "HIGH VACUUM Arthur A. Landfors,Boston, Mass., assignor to National Research Corporation, Cambridge,Mass., a corporation of Massachusetts ma Mar. 4, 195 9, Ser.No. 797,99 4c ai s. 01. 230-49 This invention relates to high vacuum pumping andmore particularly to gettering-type pumps. This invention isparticularly directed to a novel means of supporting the filament aroundwhich gettering material is positioned.

A principal object of the present invention is to provide a means ofsupport whereby filaments may be protected from stresses due toexpansion.

Another object of the invention is to provide a pumping component for avacuum system which may be readily and efliciently removed, replaced,and serviced.

A further object is to provide an inexpensive device for getter pumping.

An important object of the invention is to allow for dependability andlong life of filaments.

In the use of filaments supporting helically wound gettering materials,the filaments are heated to fairly high temperatures and are thussubject to stresses which cause frequent failures. The present inventionprovides a means for reducing such stresses and the incidence of suchfailures by providing for a filament holder fixed at one extremity ofthe filament and movable along the axial direction of the filament atits opposite extremity so it may expand freely but move only in theaxial direction.

Another problem basic to the getter pump is that both filaments andgettering material such as tantalum must be replaced periodically. Inthe present invention a removable filament holder can be insertedthrough an aperture in the wall of a vacuum chamber and sealed to thewall by means of a flange and a gasket such as a crush ring seal. Theflange is preferably threaded so as to be connectable to a matchedthread on the wall of the chamber. Substitution or repair of such unitscan be completed with little loss of operating time.

Another factor adding to the usefulness of this device is that more thanone pumping unit can be installed in the same chamber. The pumping ratewill approximate that desired and the system will operate in spite offailure of one unit.

In a preferred form of the invention, a rod or filament of refractorymaterial is arranged to be heated to a high temperature so as tovaporize gettering material. Supports are placed at opposite ends of therod, one support being rigid and the other being movable axially so thatthe rod can move axially while being rigidly supported to withstandtransverse forces. The supports are electrically insulated from eachother. The rod is wound with gettering material such as titanium (ortantalum). The device is sealed to the chamber to be evacuated by use ofa flange and a crush ring.

The apparatus for supporting the rod comprises a metal tube with slotsthrough which vaporized gettering material may ditfuse. Preferably thetube also acts as an electrical conductor for one terminal of therefractory filament.

A preferred embodiment of the device is shown in the drawings. Figure 1is a diagrammatic, schematic, sectional view of the device attached to aportion of the chamber wall. Figure 2 is a diagrammatic, schematic,sectional view 'of the tube shown in Figure 1 along section line A-A ofFigure 1.

In Figure '1, the wall 10 of the chamber to be evacuated is arrangedwith an opening and a threaded lip'so that flange 12 may bescrewedtightly to crush ring 14 which is used to seal wall 10 and flange12. Attached to flange12 is tube 16 which is the support for the otherparts of the device. It has an opening 18 at the top and bottom topermit escape of" the getter vapors. Into one I end portion, of tube 16is placed a sliding block 20.

The filament" r'od'26 is supported 'at one end by sliding block 20 andat the other end by electrode 28. When the filament 26 expands, theblock 20 will move and there will be no stress upon the filament rod dueto such expansion. Still the filament does not move transversely. Aroundfilament 26 are windings of gettering material 24 such as tantalum ortitanium. Windings 24 may be one or more helical windings.

Electrode 28 is supported by insulating material 30 which is carried bytube 16. Tube 16 and shielding 34 are separated electrically. Insulatingmaterial 30, electrode 28, and tube 16 are vacuum sealed to each other.

The voltage source 32 is connected to electrode 28 although the actualconnection is not shown here. The current path passes through electrode28, filament 26, support 20, tube 16, and flange 12. The flange 12 ispreferably grounded.

When current passes through the circuit above described, filament 26 isheated to a temperature at which gettering material 24 is vaporized.This vaporized gettering material then passes through slits 18 andoperates to evacuate the chamber enclosed in part by wall 10.

The reaction which causes pumping is the combination of the metal orgettering material with the gases present in the chamber to beevacuated. Gettering materials include titanium, tantalum, zirconium,and other materials such as barium, magnesium and aluminum. Other modesof using the getter may be employed than a helix. The getter can bemerely placed on the filament in single closed loops which are notdislodged due to rotation of the pump.

The spirit of the invention includes other means of removably mountingthe pump to the wall of the ion chamber.

Equally the slits in the tube can be replaced by openings of diiferentshape, cross-section or size, and the mounting block can have anothershape.

Since certain changes may be made in the above apparatus withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description, or shown inthe accompanying drawing, shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:

l. A device for producing vacuum comprising a refractory rod capable ofbeing heated electrically to a high temperature, gettering materialcarried by said rod so as to be vaporized by said high temperature,supports arranged at opposite ends of said rod, one support being rigidand one being movable axially so that said rod is free to extendaxially, means for preventing transverse movement of said movablesupport, means for electrically insulating said supports from eachother, and means for connection to a wall of a vacuum chamber forforming a vacuum-tight joint with said rod and supporting said rodwithin said vacuum chamber.

2. A pump element which is adapted to be inserted through an aperture ina wall of a chamber which is to be evacuated, said element comprising asource of gettering material for mounting on a flange which seals theaperture, said device having a rigid refractory filament Patented May30, 1,961,

winding of at least onegetteringm'aterial, 'a 'pair of sup ports forsaid filament arranged so that motion transverse the x s aifi em s l m tQ t aisl fl p t ba mama t w r ea en? in i e t an alongsaid 'axis and theother of, said supports being adapted to be rigidly onnected to saidfiangef 3"."A vacuum pump comprising a refractory metalfilamentjwoundwith gettering material, two supports for said filament, a sealingflange for forming a vacuum-'tightseal with aportion of the walls of thesystem to be evacuated, afhollow cylindrical tubetwith, openingssurrounding said filament," said supports forsaid filament beingconnected by said hollow cylindrical tube so that, said openingsallowniffusion otvapor therethrough, one ofvsaid sup- 15 2,796,555

ports being rigidly connected to said tube, the other of said supportsbeing slid'ably connected to said tube to vaporized getteringmaterial-diffuses when said filament is heated, said hollow cylindricaltube further acting as 10 an electrical lead for current flowing throughfilament.

References Cited in the file of this patent UNITED STATES PATENTS ConnorJune 18, 1957

